1. Field of the Invention
The field of this invention pertains to a device and method for isoenergetic intensity modulation of a beam of charged particles, and more particularly to a device and method for iso-energetic intensity modulation of a therapeutic electron beam.
2. Description of Related Art
High energy electron beams (MeV range) have been widely used in the field of radiotherapy. The principal applications for this type of radiotherapy are for skin cancer, chest well irradiation for breast cancer, administering boost doses to nodes, and the treatment of head and neck cancers (Faiz M. Khan, The Physics of Radiation Therapy, William & Wilkins).
Modern therapy linear accelerators provide electron beams with satisfactory field flatness and symmetry of the intensity profile. However, many clinical situations indicate that an electron beam with a tilted, concave, or asymmetric intensity profile is useful for the treatment of a curved or oblique skin surface.
Photon (gamma or x-ray) beams with a tilted beam intensity profile have become common practice and is achieved by placing a wedge shaped absorber (a commercially available standard accessory) in the photon beam path. While the same principle has been attempted in order to produce a tilted electron beam profile, the technique used for photon beams causes the electron beam energy to be seriously degraded throughout the modified electron field. Thus, heretofore there has been no commercially available electron wedge filter.